When a liquid is placed in a closed container, a certain amount of headspace remains between the surface of the liquid and the container closure. In many applications, it is desirable to isolate the liquid from that headspace.
One such application of prime interest here concerns blood gas measurements which determine the pH, pCO.sub.2 and pO.sub.2 levels of blood specimens. These measurements which are carried out in most hospitals are often performed on arterial blood specimens on an emergency basis and the results used to assist in the selection of proper therapeutic measures for the particular patient.
Under these conditions, the instrumentation needed to perform the determinations is taken from a standby condition and used to perform these measurements. Accordingly it is especially important that quality control tests be performed in parallel with the patient specimens to assure that the blood gas instrumentation is providing accurate test data.
In other words, in order to assure that the instrument used to measure blood gas values on these specimens is accurate, reliable and precise, commercially prepared test samples should be run regularly as quality control samples.
Each control or test sample consists of a gas-equilibrated aqueous solution or cell system packaged in a sealed ampule or vial. The control liquid occupies the lower part of the ampule or vial and a gaseous headspace occupies the remainder of the vial. However, since the partition of the headspace vapor with the control liquid may change during storage because of variations in storage temperature, the headspace must be re-equilibrated with the control liquid in the vial immediately before using the sample in order to insure predictable levels of pH, pCO.sub.2 and pO.sub.2 of the control liquid.
This re-equilibration process is usually accomplished by vigorously shaking the vial while maintaining it at a known constant temperature. However, that procedure is troublesome for the laboratory technologist. Also, variations in the shaking technique used by the laboratory personnel can lead to inaccurate results from the blood gas measuring instrument.
An obvious solution to this problem is the complete elimination of headspace in such containers. However, this is difficult to accomplish in practice. Also, when opening such completely filled containers, it is very difficult to avoid spilling some of the container contents. Until now, then, no really effective way has been found to avoid the problem of having to re-equilibrate such blood test samples.
Organic liquid samples such as blood gas controls also have a tendency to support the growth of microorganisms which are detrimental to the effectiveness of the liquid. Therefore, it would be desirable, in addition, to inhibit such growth and thus preserve the effectiveness of the sample for a prolonged period.